Generally, the optical memory card is a plastic card and can record and reproduce data in its recording region with a laser beam.
FIG. 7 shows a recording region 102 of an optical memory card 101. As shown in its enlarged diagram, data recording tracks 103 for recording information and guide tracks 104 formed at given intervals required for tracking control for stabilizing a radiating position of the laser beams for recording and reproducing are alternately disposed on the recording region 102.
The data recording tracks 103 and the guide tracks 104 have a different reflection ratio. Comparing the reflection ratio of these two, the data recording tracks 103 have a higher reflection ratio and the guide tracks 104 have a lower reflection ratio.
And, a record pit 105 is a portion having a low reflection ratio, which is formed in the data recording tracks 103, with the laser beam to record information. The presence or not of the record pit 105 indicates information to be recorded.
FIG. 8 shows a logical data structure of the recording region 102. On the recording region 102, read-in 111 provided for an unillustrated optical memory card reader/writer to realize a bit synchronization at the time of recording or reproducing and an SYNC mark 112 for the unillustrated optical memory card reader/writer to realize a frame synchronization at the time of recording or reproducing have been recorded, in addition to a data recording region 110 where information is recorded.
The read-in 111 has the SYNC mark 112 recorded and record pits 105 formed at given intervals.
An optical memory card reader/writer (not shown) is provided with a synchronization signal generator (not shown), scans the optical memory card 101 at a scan rate so that a synchronization signal output from the synchronization signal generator agrees with a signal which rises for every one bit detected by scanning the read-in 111, and keeps the same scan rate to make bit synchronization.
And, the SYNC mark 112 is formed of record pits 105, which are arranged in a pattern not produced by modulation, and used when the unillustrated optical memory card reader/writer gets frame synchronization.
The frame is a bit separation to process a signal by a signal processing circuit in the unillustrated optical memory card reader/writer. The unillustrated optical memory card reader/writer is provided with a counter (not shown) for obtaining frame synchronization. The counter counts the synchronization signal, outputs a frame synchronization signal after counting up to the number of bits configuring one frame, and resets its counted number.
Since the SYNC mark 112 is recorded at the start end (or termination end) of the frame, the unillustrated optical memory card reader/writer scans the optical memory card 101. And when the SYNC mark 112 is detected, the number indicated by the unillustrated counter for obtaining frame synchronization is reset, thereby assuring the acquisition of frame synchronization.
And, the data recording region 110 has the SYNC mark and n sectors 113 arranged as indicated by a data recording region 110-1 on each frame. The sector 113 is composed of a single or a plurality of bits.
FIG. 9 is a diagram showing an NRZI-RZ (nonreturn-to-zero change on 1-return to zero) modulation system for converting data, which is recorded in a conventionally used optical memory card, into the presence or not of a record pit.
The NRZI-RZ modulation system is a modulation system to produce a pulse at a polarity reversion position of an NRZI (nonreturn-to-zero change on 1) modulation system.
When data shown in FIG. 9(a) is modulated, the NRZI modulation system reverses the polarity of a signal at the bit midpoint of data "1" as shown in FIG. 9(b).
Accordingly, the NRZI-RZ modulation system generates a pulse at a polarity reversion position of FIG. 9(b) as shown in FIG. 9(c).
Data modulated by the NRZI-RZ modulation system is recorded by forming a record pit in the recording region of the optical memory card so as to correspond to the position of the pulse as shown in FIG. 9(d).
As apparent from FIG. 9(a) and FIG. 9(d), the NRZI-RZ modulation system does not form a record pit on a part where data "0" is continuous.
However, before recording data on the optical memory card, the optical memory card reader/writer reproduces the optical memory card to detect the presence or not of a record pit. Thus, it judges between an unrecorded region and a recorded region of the optical memory card to prevent double writing on it. Therefore, if data to be recorded in the optical memory card has a portion where data "0" is continuous, a record pit is not formed on the optical memory card while data "0" is continuing. And, it becomes hard to judge between the unrecorded region and the recorded region, resulting in degrading a function of preventing double writing from being made by the optical memory card reader/writer.